1. Field of the Invention
This invention relates to filtering and screening devices, and more particularly relates to an apparatus for screening waste materials from a water stream.
2. Description of the Prior Art
Several prior art apparatus operable to filter and screen waste materials have been disclosed in a number of U.S. patents throughout the years. An endless screen for screening water in gate-houses of waterworks systems in which the screen may be shifted to a fresh portion by a single person is described in U.S. Pat. No. 658,196 to Whitney (1900).
An apparatus comprising a rotary screen in the form of an endless screening apron, supported upon two drums and having a series of projections to engage and lift the rubbish to the surface of the water, is disclosed in U.S. Pat. No. 677,567 to Freeman (1901).
A screen structure to arrest and remove any collection of sticks, leaves or the like in a water supply in such a manner as to prevent the screen from becoming clogged is disclosed in U.S. Pat. No. 1,207,376 to Davidson (1916). This structure comprises a screen frame, shafts journaled at the upper and lower ends of said frame and an endless screen member arranged to operate over said shafts.
A combined fish-screen and debris-remover which comprises a series of members arranged in an endless chain and means for moving said members orbitally in a vertical plane is described in U.S. Pat. No. 1,252,617 to Requa (1918).
A flume screen that reduces the leakage of the unscreened liquid past the submerged ends of the screen is disclosed in U.S. Pat. No. 1,514,673 to Roddy (1924). This screen of an endless, traveling type comprises screen sections and sprocket chains to which the ends of the screen sections are secured, the combination with the submerged end of the screen and the means that cause it to make the lower turn, of means arranged to cover the lateral edges of the screen and the chains to restrict the flow of unscreened water around the side edges of the screen, and guards inside the restricting means arranged close to and opposite the outer edges of the supporting chains arranged to restrict the passage of the unfiltered water that may escape around the edges of the screen through the chains.
A screening and filtering apparatus, described in U.S. Pat. No. 1,967,050 to Brackett (1934), discloses perforated or mesh plates made in sections and secured together by terminal flanges forming stiffening bars projecting on one side and running transversely across the plates. The plates may be secured to the side chains by angle pieces bolted to the plates and to the links.
An apparatus for cleaning bar grids, as described in U.S. Pat. No. 3,856,216 to Teague et. al. (1974), discloses an automatic rake provided with a plurality of fingers extending between the bars of the grid so that the material from the grid will be raked into the path of a disintegrator to be pulverized therein.
A rotary filter apparatus having an endless belt composed of many linking rods, linking plates, wire ropes or screen plates, and specially-shaped filter plates rockably fitted on the transverse linking rods, is disclosed in U.S. Pat. No. 4,188,294 to Hagihara (1980).
Filter and screening devices in the art today encounter many operational difficulties because of their shortcomings and limitations. For example, filtering devices for fine screening are susceptible to the blanking of the screen openings. This causes a water head increase upstream of the device location. Because of the sticky nature of the waste materials, other auxiliary devices are sometimes needed to dislodge the blanking material or to unplug the screen opening of such filtering devices. Examples of these auxiliary devices are water sprays, combing devices and rotating brushes. The use of such devices requires a significant increase of electrical power for their operation. Moreover, the effectiveness of these devices is considerably low.
Furthermore, some filtering and screening devices in the market provide for dual filtration. This is necessary since at the bottom end of these devices their filter elements require an open space for making the turn. This is an undesirable feature because larger and heavier waste materials tends to roll along the bottom of the flow stream channel and slip through the large open spaces located there.
Another difficulty with conventional filtering devices arises when materials to be screened protrudes through the screen openings. These materials cause damage to both the screening elements and the driving mechanism of such filtering devices.
There is a need for an apparatus that filters and screens waste materials from a water stream in an economical and effective way without the use of auxiliary devices for unplugging the screening openings and dislodging the materials therein.
It is therefore an object of this invention to provide a filtering apparatus that effectively cleans the screening elements during the filtering and screening action.
It is another object of this invention to provide a filtering apparatus that prevents the waste materials from bypassing the screening elements at the bottom end of the apparatus.
It is another object of this invention to provide a filtering apparatus that effectively dislodges the waste materials protruding through the screen openings, thereby preventing damage to the apparatus.
It is still another object of this invention to provide a filtering apparatus having a simple design with no drag chains, chain links, bearings, or sprockets subject to submersion.